Potential applications of carbon nanotubes
Encyclopedia
Carbon nanotube
s, a type of fullerene
, have potential in fields such as nanotechnology
, electronics
, optics
, materials science
, and architecture
. Over the years
new applications have taken advantage of their unique electrical
properties, extraordinary strength, and efficiency in heat conduction
.
s end to end can act as a diode
, suggesting the possibility of constructing computer circuits entirely of nanotubes. Because of their good thermal transmission properties, CNT can potentially dissipate heat from computer chips. The longest electricity conducting circuit is a fraction of an inch long.
Fabrication difficulties are major hurdles for CNT. Standard IC fabrication processes use chemical vapor deposition
to add layers to a wafer. CNT can so far not be mass produced using such techniques.
Researchers can manipulate nanotubes one-by-one with the tip of an atomic force microscope
in a time-consuming process. Using standard fabrication techniques would still require designers to position one end of the nanotube. During the deposition process, an electric field
can potentially direct the growth of the nanotubes, which tend to grow along the field lines from negative to positive polarity. Another technique for self-assembly uses chemical or biological techniques to move CNT in solution to determinate places on a substrate.
Even if nanotubes can be precisely positioned, engineers have been unable to control the types (conducting, semiconducting, SWNT, MWNT) of nanotubes that appear.
as very-large-scale integration
(VLSI) interconnects because of their high thermal stability
, high thermal conductivity
and large current carrying capacity. An isolated CNT can carry current
densities in excess of 1000 MA/sq-cm without damage even at an elevated temperature of 250 °C (482 °F), eliminating electromigration reliability concerns that plague Cu
interconnects. Recent modeling work comparing the two has shown that CNT bundle interconnects can potentially offer advantages over copper. Recent experiments demonstrated resistances as low as 20 Ohms
using different architectures, detailed conductance measurements over a wide temperature range were shown to agree with theory for a strongly disordered quasi-one-dimensional conductor.
Hybrid interconnects that employ CNT vias in tandem with copper interconnects offers advantages from a reliability/thermal-management perspective.
s. Since the electron mean free path in SWCNTs can exceed 1 micrometer, long channel CNTFETs exhibit near-ballistic transport
characteristics, resulting in high speed devices. CNT devices are projected to operate in the frequency range of hundreds of Gigaherz. Recent work detailing the advantages and disadvantages of various forms of CNTFETs have also shown that tunneling CNTFET offers better characteristics compared to other CNTFET structures. This device has been found to be superior in terms of subthreshold slope - a very important property for low power applications.
Nanotubes are usually grown on nanoparticles of magnetic metal (Fe
, Co
) that facilitates production of electronic (spintronic) devices. In particular control of current through a field-effect transistor by magnetic field has been demonstrated in such a single-tube nanostructure.
substrate
as a back gate. Applying different back gate voltage
s might become a concern when designing large circuits out of these elements. Several top-gated structures have also been demonstrated, which can alleviate this concern. Recently, a fully integrated logic circuit built on a single nanotube was reported. This circuit employs a back-gate. Several process-related challenges need to be addressed before CNT-based devices and interconnects can enter mainstream VLSI manufacturing. Remaining problems include purification, separation, control over length, chirality and desired alignment, low thermal budget and high contact resistance. Innovative ideas have been proposed to build practical transistors out of nano-networks. Since lack of control on chirality produces a mix of metallic as well as semi-conducting CNTs from any fabrication process and it is difficult to control the growth direction of the CNTs, easily-produced random arrays of SWCNTs have been proposed to build thin film transistors. This idea can be further exploited to build practical CNT based transistors and circuits without the need for precise growth and assembly.
proliferation and bone formation.
Carbon nanotube
Carbon nanotubes are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, significantly larger than for any other material...
s, a type of fullerene
Fullerene
A fullerene is any molecule composed entirely of carbon, in the form of a hollow sphere, ellipsoid, or tube. Spherical fullerenes are also called buckyballs, and they resemble the balls used in association football. Cylindrical ones are called carbon nanotubes or buckytubes...
, have potential in fields such as nanotechnology
Nanotechnology
Nanotechnology is the study of manipulating matter on an atomic and molecular scale. Generally, nanotechnology deals with developing materials, devices, or other structures possessing at least one dimension sized from 1 to 100 nanometres...
, electronics
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...
, optics
Optics
Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...
, materials science
Materials science
Materials science is an interdisciplinary field applying the properties of matter to various areas of science and engineering. This scientific field investigates the relationship between the structure of materials at atomic or molecular scales and their macroscopic properties. It incorporates...
, and architecture
Architecture
Architecture is both the process and product of planning, designing and construction. Architectural works, in the material form of buildings, are often perceived as cultural and political symbols and as works of art...
. Over the years
Timeline of carbon nanotubes
-1952:* Radushkevich and Lukyanovich publish a paper in the Soviet Journal of Physical Chemistry showing hollow graphitic carbon fibers that are 50 nanometers in diameter.-1960:...
new applications have taken advantage of their unique electrical
Electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...
properties, extraordinary strength, and efficiency in heat conduction
Heat conduction
In heat transfer, conduction is a mode of transfer of energy within and between bodies of matter, due to a temperature gradient. Conduction means collisional and diffusive transfer of kinetic energy of particles of ponderable matter . Conduction takes place in all forms of ponderable matter, viz....
.
Structural
Carbon nanotubes have valuable qualities as structural materials. Potential uses include:- Textiles—CNT can make waterproof and/or tear-resistant fabrics
- Body armor—MIT is working on combat jackets that use CNT fibers to stop bullets and to monitor the condition of the wearer. Cambridge University developed the fibres and licensed a company to make them.
- ConcreteConcreteConcrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...
—CNT in concrete increase its tensile strength, and halt crack propagation. - PolyethylenePolyethylenePolyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...
—Adding CNT to polyethylene can increase the polymer's elastic modulusElastic modulusAn elastic modulus, or modulus of elasticity, is the mathematical description of an object or substance's tendency to be deformed elastically when a force is applied to it...
by 30%. - Sports equipment—Stronger and lighter tennis rackets, bicycleBicycleA bicycle, also known as a bike, pushbike or cycle, is a human-powered, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A person who rides a bicycle is called a cyclist, or bicyclist....
parts, golf ballGolf ballA golf ball is a ball designed to be used in the game of golf.Under the Rules of Golf, a golf ball weighs no more than 1.620 oz , has a diameter not less than 1.680 in , and performs within specified velocity, distance, and symmetry limits...
s, golf clubGolf clubA golf club is used to hit a golf ball in a game of golf. Each club is composed of a shaft with a grip and a clubhead. Woods are mainly used for long-distance fairway or tee shots; irons, the most versatile class, are used for a variety of shots; Hybrids that combine design elements of woods and...
s, and baseball batBaseball batA baseball bat is a smooth wooden or metal club used in the game of baseball to hit the ball after the ball is thrown by the pitcher. It is no more than 2.75 inches in diameter at the thickest part and no more than 42 inches in length. It typically weighs no more than 33 ounces , but it...
s. - Space elevatorSpace elevatorA space elevator, also known as a geostationary orbital tether or a beanstalk, is a proposed non-rocket spacelaunch structure...
—CNT are under investigation as possible components of the tetherTetherA tether is a cord, fixture, or signal that anchors something movable to a reference point which may be fixed or moving. There are a number of applications for tethers: balloons, kites, tethered wind-energy conversion systems, anchors, tethered water-flow energy conversion systems, towing, animal...
up which a space elevator can climb. This requires tensile strengthTensile strengthUltimate tensile strength , often shortened to tensile strength or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract...
s of more than about 70 GPa. - synthetic musclesElectroactive polymersElectroactive Polymers, or EAPs, are polymers that exhibit a change in size or shape when stimulated by an electric field. The most common applications of this type of material are in actuators and sensors. A typical characteristic property of an EAP is that they will undergo a large amount of...
: Due to their high contraction/extension ratio given an electric current, CNTs are ideal for synthetic muscle. - High tensile strengthTensile strengthUltimate tensile strength , often shortened to tensile strength or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract...
fiberFiberFiber is a class of materials that are continuous filaments or are in discrete elongated pieces, similar to lengths of thread.They are very important in the biology of both plants and animals, for holding tissues together....
s—Fibers produced with polyvinyl alcoholPolyvinyl alcoholPolyvinyl alcohol is a water-soluble synthetic polymer .-Properties:...
required 600 J/g to break. In comparison, the bullet-resistant fiber KevlarKevlarKevlar is the registered trademark for a para-aramid synthetic fiber, related to other aramids such as Nomex and Technora. Developed at DuPont in 1965, this high strength material was first commercially used in the early 1970s as a replacement for steel in racing tires...
fails at 27–33 J/g. - Bridges—CNT may be able to replace steel in suspension and other bridges.
- FlywheelFlywheelA flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels have a significant moment of inertia, and thus resist changes in rotational speed. The amount of energy stored in a flywheel is proportional to the square of its rotational speed...
s—The high strength/weight ratio enables very high rotational speeds. - Carbon nanotube springsCarbon nanotube springsCarbon nanotube springs are springs made of carbon nanotubes . They are an alternate form of high density, lightweight, reversible energy storage based on the elastic deformations of CNTs. Many previous studies on the mechanical properties of CNTs have revealed that they possess high stiffness,...
—Single-walled carbon nanotubes aligned in parallel can be elastically stretched for an energy density 10 times greater than that of current lithium-ion batteries, with the additional advantages of long cycling durability, temperature insensitivity, no spontaneous dischange, and arbitrary discharge rate. - Fire protection—Thin layers of buckypaperBuckypaperBuckypaper is a thin sheet made from an aggregate of carbon nanotubes. The nanotubes are approximately 50,000 times thinner than a human hair. Originally, it was fabricated as a way to handle carbon nanotubes, but it is also being studied and developed into applications by several research groups,...
can significantly improve fire resistance due to the efficient reflection of heat by the dense, compact layer of CNT or carbon fiberCarbon fiberCarbon fiber, alternatively graphite fiber, carbon graphite or CF, is a material consisting of fibers about 5–10 μm in diameter and composed mostly of carbon atoms. The carbon atoms are bonded together in crystals that are more or less aligned parallel to the long axis of the fiber...
s.
Electromagnetic
CNT can be fabricated as electrical conductors, insulators, and semiconductors. Applications include:- Artificial musclesElectroactive polymersElectroactive Polymers, or EAPs, are polymers that exhibit a change in size or shape when stimulated by an electric field. The most common applications of this type of material are in actuators and sensors. A typical characteristic property of an EAP is that they will undergo a large amount of...
—CNT's have sufficient contractility to make them candidates to replace muscle tissue. - BuckypaperBuckypaperBuckypaper is a thin sheet made from an aggregate of carbon nanotubes. The nanotubes are approximately 50,000 times thinner than a human hair. Originally, it was fabricated as a way to handle carbon nanotubes, but it is also being studied and developed into applications by several research groups,...
—Thin nanotube sheets are 250 times stronger than steel and 10 times lighter and could be used as a heat sinkHeat sinkA heat sink is a term for a component or assembly that transfers heat generated within a solid material to a fluid medium, such as air or a liquid. Examples of heat sinks are the heat exchangers used in refrigeration and air conditioning systems and the radiator in a car...
for chipboards, a backlight for LCD screens or as a faraday cageFaraday cageA Faraday cage or Faraday shield is an enclosure formed by conducting material or by a mesh of such material. Such an enclosure blocks out external static and non-static electric fields...
to protect electrical devices/aeroplanes. - Chemical nanowires—CNTs can be used to produce nanowires of other elements/molecules, such as goldGoldGold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
or zinc oxideZinc oxideZinc oxide is an inorganic compound with the formula ZnO. It is a white powder that is insoluble in water. The powder is widely used as an additive into numerous materials and products including plastics, ceramics, glass, cement, rubber , lubricants, paints, ointments, adhesives, sealants,...
. These nanowires in turn can be used to cast nanotubes of other chemicals, such as gallium nitride. These can have very different properties from CNTs—for example, gallium nitride nanotubes are hydrophilicHydrophileA hydrophile, from the Greek "water" and φιλια "love," is a molecule or other molecular entity that is attracted to, and tends to be dissolved by water. A hydrophilic molecule or portion of a molecule is one that has a tendency to interact with or be dissolved by, water and other polar substances...
, while CNTs are hydrophobicHydrophobeIn chemistry, hydrophobicity is the physical property of a molecule that is repelled from a mass of water....
, giving them possible uses in organic chemistry. - Conductive films— Canatu of Helsinki, Finland, Eikos IncEikosEikos, Inc is a technology company based in Franklin, Massachusetts that is developing transparent, electrically conductive carbon nanotube films and nanotube inks for transparent conductive coatings. Eikos has branded its technology as Invisicon...
of Franklin, Massachusetts and Unidym Inc. of Silicon Valley are developing transparent, electrically conductive CNT films and NanoBuds to replace indium tin oxideIndium tin oxideIndium tin oxide is a solid solution of indium oxide and tin oxide , typically 90% In2O3, 10% SnO2 by weight. It is transparent and colorless in thin layers while in bulk form it is yellowish to grey...
(ITO) in LCDs, touch screens, and photovoltaic devices. Nanotube films show promise for use in displays for computers, cell phones, Personal digital assistantPersonal digital assistantA personal digital assistant , also known as a palmtop computer, or personal data assistant, is a mobile device that functions as a personal information manager. Current PDAs often have the ability to connect to the Internet...
s, and automated teller machineAutomated teller machineAn automated teller machine or automatic teller machine, also known as a Cashpoint , cash machine or sometimes a hole in the wall in British English, is a computerised telecommunications device that provides the clients of a financial institution with access to financial transactions in a public...
s. - Electric motor brushes—Conductive CNTs are used in brushBrush (electric)A brush is a device which conducts current between stationary wires and moving parts, most commonly in a rotating shaft. Typical applications include electric motors, alternators and electric generators.-Etymology:...
es for commercial electric motors. They replace traditional carbon blackCarbon blackCarbon black is a material produced by the incomplete combustion of heavy petroleum products such as FCC tar, coal tar, ethylene cracking tar, and a small amount from vegetable oil. Carbon black is a form of amorphous carbon that has a high surface-area-to-volume ratio, although its...
. The nanotubes improve electrical and thermal conductivity because they stretch through the plastic matrix of the brush. This permits the carbon filler to be reduced from 30% down to 3.6%, so that more matrix is present in the brush. Nanotube composite motor brushes are better-lubricated (from the matrix), cooler-running (both from better lubrication and superior thermal conductivity), less brittle (more matrix, and fiber reinforcement), stronger and more accurately moldable (more matrix). Since brushes are a critical failure point in electric motors, and also don't need much material, they became economical before almost any other application. - Light bulb filament: alternative to tungsten filaments in incandescent lampsIncandescent light bulbThe incandescent light bulb, incandescent lamp or incandescent light globe makes light by heating a metal filament wire to a high temperature until it glows. The hot filament is protected from air by a glass bulb that is filled with inert gas or evacuated. In a halogen lamp, a chemical process...
. - MagnetMagnetA magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets.A permanent magnet is an object...
s—Multi-walled nanotubes (MWNTMwntMwnt is a very small community and ancient parish in south Ceredigion, Wales, on the Irish Sea coast about 4.5 miles from Cardigan. It gets its name from the prominent steep conical hill, a landmark from much of Cardigan Bay, that rises above the beach....
coated with magnetiteMagnetiteMagnetite is a ferrimagnetic mineral with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. The chemical IUPAC name is iron oxide and the common chemical name is ferrous-ferric oxide. The formula for magnetite may also be written as FeO·Fe2O3, which is one part...
can generate strong magnetic fields.) - Optical ignition—A layer of 29% iron enriched single-walled nanotubes (SWNT) is placed on top of a layer of explosive material such as PETNPETNPentaerythritol tetranitrate , also known as PENT, PENTA, TEN, corpent, penthrite , is the nitrate ester of pentaerythritol. Penta refers to the five carbon atoms of the neopentane skeleton.PETN is most well known as an explosive...
, and can be ignited with a regular camera flash. - Solar cells—GE's CNT diode exploits a photovoltaic effect. Nanotubes can replace ITO in some solar cells to act as a transparent conductive film in solar cells to allow light to pass to the active layers and generate photocurrent.
- Superconductor—Nanotubes have been shown to be superconductingSuperconductivitySuperconductivity is a phenomenon of exactly zero electrical resistance occurring in certain materials below a characteristic temperature. It was discovered by Heike Kamerlingh Onnes on April 8, 1911 in Leiden. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum...
at low temperatures. - Ultracapacitors—MIT is researching the use of nanotubes bound to the charge plates of capacitorCapacitorA capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
s in order to dramatically increase the surface area and therefore energy storage ability. - Displays—CNTs can be used as extremely fine electron gunElectron gunAn electron gun is an electrical component that produces an electron beam that has a precise kinetic energy and is most often used in television sets and computer displays which use cathode ray tube technology, as well as in other instruments, such as electron microscopes and particle...
s, which could be used as miniature cathode ray tubeCathode ray tubeThe cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
s in thin high-brightness, low-energy, low-weight displays. This type of display would consist of a group of many tiny CRTs, each providing the electronElectronThe electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s to hit the phosphorPhosphorA phosphor, most generally, is a substance that exhibits the phenomenon of luminescence. Somewhat confusingly, this includes both phosphorescent materials, which show a slow decay in brightness , and fluorescent materials, where the emission decay takes place over tens of nanoseconds...
of one pixelPixelIn digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....
, instead of having one giant CRT whose electrons are aimed using electric and magnetic fieldMagnetic fieldA magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
s. These displays are known as field emission displayField emission displayA field emission display is a display technology that incorporates flat panel display technology that uses large-area field electron emission sources to provide electrons that strike colored phosphor to produce a color image as a electronic visual display...
s (FEDs). - TransistorTransistorA transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...
—CNT transistors have been developed at Delft, IBM, and NEC. - Electromagnetic antennaAntenna (radio)An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
—CNTs can act as antennas for radios and other electromagneticElectromagnetismElectromagnetism is one of the four fundamental interactions in nature. The other three are the strong interaction, the weak interaction and gravitation...
devices.
Electroacoustic
- LoudspeakerLoudspeakerA loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...
—In November, 2008 TsinghuaTsinghua UniversityTsinghua University , colloquially known in Chinese as Qinghua, is a university in Beijing, China. The school is one of the nine universities of the C9 League. It was established in 1911 under the name "Tsinghua Xuetang" or "Tsinghua College" and was renamed the "Tsinghua School" one year later...
-FoxconnFoxconnThe Foxconn Technology Group is a multinational business group anchored by the Hon Hai Precision Industry Co., Ltd. , a Taiwan-registered corporation headquartered in Tucheng, Taiwan...
Nanotechnology Research Centre in Beijing announced that it had created loudspeakerLoudspeakerA loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...
s from sheets of parallel CNT, generating sound similar to how lightning produces thunderThunderThunder is the sound made by lightning. Depending on the nature of the lightning and distance of the listener, thunder can range from a sharp, loud crack to a long, low rumble . The sudden increase in pressure and temperature from lightning produces rapid expansion of the air surrounding and within...
. Near-term commercial uses include replacing piezoelectricPiezoelectricityPiezoelectricity is the charge which accumulates in certain solid materials in response to applied mechanical stress. The word piezoelectricity means electricity resulting from pressure...
speakers in greeting cardGreeting cardA greeting card is an illustrated, folded card featuring an expression of friendship or other sentiment. Although greeting cards are usually given on special occasions such as birthdays, Christmas or other holidays, they are also sent to convey thanks or express other feeling. Greeting cards,...
s.
Chemical
- DesalinationDesalinationDesalination, desalinization, or desalinisation refers to any of several processes that remove some amount of salt and other minerals from saline water...
— water molecules can be separated from salt by forcing them through networks of carbon nanotubes, which require far lower pressures than conventional reverse osmosisReverse osmosisReverse osmosis is a membrane technical filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side of a selective membrane. The result is that the solute is retained on the pressurized side of the membrane and...
methods - Air pollutionAir pollutionAir pollution is the introduction of chemicals, particulate matter, or biological materials that cause harm or discomfort to humans or other living organisms, or cause damage to the natural environment or built environment, into the atmosphere....
filterAir filterA particulate air filter is a device composed of fibrous materials which removes solid particulates such as dust, pollen, mold, and bacteria from the air. A chemical air filter consists of an absorbent or catalyst for the removal of airborne molecular contaminants such as volatile organic compounds...
—CNT membranes can filter carbon dioxideCarbon dioxideCarbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
from power plant emissions. - Biotech container—CNT can be filled with biological molecules, aiding biotechnologyBiotechnologyBiotechnology is a field of applied biology that involves the use of living organisms and bioprocesses in engineering, technology, medicine and other fields requiring bioproducts. Biotechnology also utilizes these products for manufacturing purpose...
. - HydrogenHydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
storage—CNT have the potential to store between 4.2 and 65% hydrogen by weight. If they can be mass produced economically, 13.2 litres (27.9 US pt) of CNT could contain the same amount of energy as a 50 litres (105.7 US pt) gasoline tank. See Hydrogen EconomyHydrogen economyThe hydrogen economy is a proposed system of delivering energy using hydrogen. The term hydrogen economy was coined by John Bockris during a talk he gave in 1970 at General Motors Technical Center....
.
Mechanical
- Oscillator—Oscillators based on CNT have achieved higher speeds than other technologies (> 50 GHzGHZGHZ or GHz may refer to:# Gigahertz .# Greenberger-Horne-Zeilinger state — a quantum entanglement of three particles.# Galactic Habitable Zone — the region of a galaxy that is favorable to the formation of life....
). - Nanotube membraneNanotube membraneNanotube membrane is either a single, open-ended nanotube or a film composed of open-ended nanotubes that are oriented perpendicularly to the surface of an impermeable film matrix like the cells of a honeycomb. 'Impermeable' is essential here to distinguish nanotube membrane with traditional, well...
—Liquid flows up to five orders of magnitude faster than predicted by classical fluid dynamicsFluid dynamicsIn physics, fluid dynamics is a sub-discipline of fluid mechanics that deals with fluid flow—the natural science of fluids in motion. It has several subdisciplines itself, including aerodynamics and hydrodynamics...
. - Slick surface—Some CNT-based fabrics have shown lower friction than Teflon.
- Waterproof—Some CNT-fabrics are waterproof.
- Carbon nanotube actuatorsCarbon nanotube actuatorsThe exceptional electrical and mechanical properties of carbon nanotubes have made them alternatives to the traditional electrical actuators for both microscopic and macroscopic applications. Carbon nanotubes are very good conductors of both electricity and heat, and they are also very strong and...
— - Infrared detectorInfrared detectorAn infrared detector is a photodetector that reacts to infrared radiation. The two main types of detectors are thermal and photonic.The thermal effects of the incident IR radiation can be followed through many temperature dependent phenomena....
—The reflectivity of the buckypaperBuckypaperBuckypaper is a thin sheet made from an aggregate of carbon nanotubes. The nanotubes are approximately 50,000 times thinner than a human hair. Originally, it was fabricated as a way to handle carbon nanotubes, but it is also being studied and developed into applications by several research groups,...
produced with "super-growth" chemical vapor depositionChemical vapor depositionChemical vapor deposition is a chemical process used to produce high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films. In a typical CVD process, the wafer is exposed to one or more volatile precursors, which react and/or...
method is 0.03 or less, potentially enabling performance gains for pyroelectric infrared detectorInfrared detectorAn infrared detector is a photodetector that reacts to infrared radiation. The two main types of detectors are thermal and photonic.The thermal effects of the incident IR radiation can be followed through many temperature dependent phenomena....
.
- Radiometric standard—As a standard of the black.
- Thermal radiationThermal radiationThermal radiation is electromagnetic radiation generated by the thermal motion of charged particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation....
—For thermal emission in space such as space satellites. - stealthStealth technologyStealth technology also termed LO technology is a sub-discipline of military tactics and passive electronic countermeasures, which cover a range of techniques used with personnel, aircraft, ships, submarines, and missiles, to make them less visible to radar, infrared, sonar and other detection...
—Absorbance is high in wide ranges from FUV to FIR.
Electrical circuits
A nanotube formed by joining two nanotubes of different diameterDiameter
In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle...
s end to end can act as a diode
Diode
In electronics, a diode is a type of two-terminal electronic component with a nonlinear current–voltage characteristic. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material connected to two electrical terminals...
, suggesting the possibility of constructing computer circuits entirely of nanotubes. Because of their good thermal transmission properties, CNT can potentially dissipate heat from computer chips. The longest electricity conducting circuit is a fraction of an inch long.
Fabrication difficulties are major hurdles for CNT. Standard IC fabrication processes use chemical vapor deposition
Chemical vapor deposition
Chemical vapor deposition is a chemical process used to produce high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films. In a typical CVD process, the wafer is exposed to one or more volatile precursors, which react and/or...
to add layers to a wafer. CNT can so far not be mass produced using such techniques.
Researchers can manipulate nanotubes one-by-one with the tip of an atomic force microscope
Atomic force microscope
Atomic force microscopy or scanning force microscopy is a very high-resolution type of scanning probe microscopy, with demonstrated resolution on the order of fractions of a nanometer, more than 1000 times better than the optical diffraction limit...
in a time-consuming process. Using standard fabrication techniques would still require designers to position one end of the nanotube. During the deposition process, an electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
can potentially direct the growth of the nanotubes, which tend to grow along the field lines from negative to positive polarity. Another technique for self-assembly uses chemical or biological techniques to move CNT in solution to determinate places on a substrate.
Even if nanotubes can be precisely positioned, engineers have been unable to control the types (conducting, semiconducting, SWNT, MWNT) of nanotubes that appear.
Interconnects
Metallic carbon nanotubes have aroused research interest for their applicabilityas very-large-scale integration
Very-large-scale integration
Very-large-scale integration is the process of creating integrated circuits by combining thousands of transistors into a single chip. VLSI began in the 1970s when complex semiconductor and communication technologies were being developed. The microprocessor is a VLSI device.The first semiconductor...
(VLSI) interconnects because of their high thermal stability
Thermal stability
Thermal stability is the stability of a molecule at high temperatures; i.e. a molecule with more stability has more resistance to decomposition at high temperatures....
, high thermal conductivity
Thermal conductivity
In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....
and large current carrying capacity. An isolated CNT can carry current
densities in excess of 1000 MA/sq-cm without damage even at an elevated temperature of 250 °C (482 °F), eliminating electromigration reliability concerns that plague Cu
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
interconnects. Recent modeling work comparing the two has shown that CNT bundle interconnects can potentially offer advantages over copper. Recent experiments demonstrated resistances as low as 20 Ohms
Ohms
OHMS may refer to:* The plural of ohm, a unit of resistance, named after Georg Ohm* Ohm's Law of electric currents, first proposed by Georg Ohm* O.H.M.S., On His/Her Majesty's Service...
using different architectures, detailed conductance measurements over a wide temperature range were shown to agree with theory for a strongly disordered quasi-one-dimensional conductor.
Hybrid interconnects that employ CNT vias in tandem with copper interconnects offers advantages from a reliability/thermal-management perspective.
Transistors
Semiconducting CNTs have been used to fabricate field effect transistors (CNTFETs), which show promise due to their superior electrical characteristics over silicon based MOSFETMOSFET
The metal–oxide–semiconductor field-effect transistor is a transistor used for amplifying or switching electronic signals. The basic principle of this kind of transistor was first patented by Julius Edgar Lilienfeld in 1925...
s. Since the electron mean free path in SWCNTs can exceed 1 micrometer, long channel CNTFETs exhibit near-ballistic transport
Ballistic transport
Ballistic transport is the transport of electrons in a medium with negligible electrical resistivity due to scattering. Without scattering, electrons simply obey Newton's second law of motion at non-relativistic speeds....
characteristics, resulting in high speed devices. CNT devices are projected to operate in the frequency range of hundreds of Gigaherz. Recent work detailing the advantages and disadvantages of various forms of CNTFETs have also shown that tunneling CNTFET offers better characteristics compared to other CNTFET structures. This device has been found to be superior in terms of subthreshold slope - a very important property for low power applications.
Nanotubes are usually grown on nanoparticles of magnetic metal (Fe
FE
Fe or FE may refer to:* Iron * Fe , the f-rune of the Younger Futhark* Fe * Fe * "Fe" , a song by Jorge González...
, Co
Cobalt
Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal....
) that facilitates production of electronic (spintronic) devices. In particular control of current through a field-effect transistor by magnetic field has been demonstrated in such a single-tube nanostructure.
Electronic design and design automation
Although CNT devices and interconnects separately have been shown to be promising in their own respects, there have been few efforts to combine them in a realistic circuit. Most CNTFET structures employ the siliconSilicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
substrate
Substrate (semiconductor)
Substrate is a solid substance onto which a layer of another substance is applied, and to which that second substance adheres. In solid-state electronics, this term refers to a thin slice of material such as silicon, silicon dioxide, aluminum oxide, sapphire, germanium, gallium arsenide , an alloy...
as a back gate. Applying different back gate voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
s might become a concern when designing large circuits out of these elements. Several top-gated structures have also been demonstrated, which can alleviate this concern. Recently, a fully integrated logic circuit built on a single nanotube was reported. This circuit employs a back-gate. Several process-related challenges need to be addressed before CNT-based devices and interconnects can enter mainstream VLSI manufacturing. Remaining problems include purification, separation, control over length, chirality and desired alignment, low thermal budget and high contact resistance. Innovative ideas have been proposed to build practical transistors out of nano-networks. Since lack of control on chirality produces a mix of metallic as well as semi-conducting CNTs from any fabrication process and it is difficult to control the growth direction of the CNTs, easily-produced random arrays of SWCNTs have been proposed to build thin film transistors. This idea can be further exploited to build practical CNT based transistors and circuits without the need for precise growth and assembly.
Medicine
Research at University of California, Riverside has shown that carbon nanotubes are suitable scaffold materials for osteoblastOsteoblast
Osteoblasts are mononucleate cells that are responsible for bone formation; in essence, osteoblasts are specialized fibroblasts that in addition to fibroblastic products, express bone sialoprotein and osteocalcin.Osteoblasts produce a matrix of osteoid, which is composed mainly of Type I collagen...
proliferation and bone formation.
External links
- Lecture by Ray Baughman (YouTube)
- Applications of Carbon Nanotubes